I have tanks that have housed everything from bugs to snakes to saltwater fish before and have never had a problem. As long as you give the tank a good cleaning using a bleach solution of one part bleach to 10 parts water the tank should be safe no matter what type of animal was kept in it before. Once I have cleaned a tank up to my satisfaction I rinse it real good with freshwater and I personally fill it to the top and give it a double dose of Prime to remove any left over chlorine bleach. Sometimes a good soaking in a vinegar water solution is needed to help remove mineral build ups and if the tank is glass a single sided razor blade can be very helpful in removing the build up but I don’t recommend using a razor blade on an acrylic tank because they are easily scratched.